Spheroidizing s. a. e. 2300 series steels



Patented May 22, 1945 UNITED fs'r 'rEs PATENT orrlca 2,376,454 srnnaomrzmo s. a. n. 2300 snmns's'rms Herbert-H. schneiden-East Cleveland, Ohio, as-

signor to The American Steel and Wire. Com-- pany of New Jersey, a corporation of New Jersey No Drawing. Application September 21. 1948,

Serial No. 503,280

1 Claim. (c1. 148-2155) This invention is concerned with spheroidizing steel of the S. A. E. 2300 series, containing from 20% to .45% carbon, the object being to provide the in the shortest possible time, with asood working and forming properties as are obtained by the prior art method of holding the steel slightly below its critical temperature for a prolonged timeaperlod.

According to the invention, steel, coming within the deflnedclassiflcation. is heated above its Ael temperature but not above a temperature causing rapid production austenite, and is held within this range for a time producing at least some austenite while preservin substantial amounts oi pearlite. In this connection, the

pearlite may lose its lamellar appearance but substantial amounts of carbides; as microscopically visible undissolved particles, must be pre-',

served. v Y

The next step is to cool the steel at a rate at least asiast as 25' F. per hour, and preferably as last as possible, to within the temperature range where austenlte transforms to :flne pearlite, bainite, ora mixture or these structures, the steel being held within this range until the austenite, formed during the heating of the steel above its 'Aei temperature, trans iorms. In most instances the steel has suiilcient mass so that the" cooling is sumcientlyslow to directly produce the described transformation, the amount of austenite contained by the steel being restricted, by

' ture.

hem as close to its Ael tempe rature as it surely can without danger oi going over this tempera- ,The time required for complete spheroidisation will be found to be very much shorter than would be expected, yet the steel will have as good working and forming properties as if it had been. sphe- I roidized completely by the time honored method 01' the single step 01 holding the steel slightly.

below its critical, it being understood that'this old method normally produces better results than can consistently be obtained in the case oi! most shortened spheroidizing treatments. In many instances, properties obtained, by the present invention are better than those obtained by this prlorartmethod.

As a specific example of the invention, 8. A. E. 2330 steel is heated towithin the range-pi from 1210 to 1250 F. and is heldyithin this range for ironi two to i'our hours. the steel then being cooled at a rate at least as fast as 25 1''. per hour to at least 1060 l. but not so low as to produce martensite, after which the steel is reheated to within the range or from 1150'F. to 1180 1 and held within this range for from four to six hours, all as required toeflect complete spheroidization.

' As specific temperatures, 1230" I". may be used the need for preserving substantial amounts of n fil'iite. during the heating above the Aei temp rature.

Summarizing the two preceding paragraphs. the idea is to'produoe relatively small amounts of austenite in the steel while preserving substantial amounts otits pearlite, and to then quench the steel to transform this austenite-i'c a relatively hard structure, as compared to annealed and spherotdizedstructures. other than martensite.

In all events, care must be taken to avoid pro-' v.duction or martensite. It appears that heating the steel very much above its -Ae1 temper-shire favors the production of martenslte, and this is another reason ior'heating the steel to very slightly above this temperature. still another reason being the desire to avoid the rapid production of austenite, so as to provide relatively extended permissible time during whic small amounts oi .austenite are produced-without the lossot too for holding thesteel to slightly austenitize it while preserving its pearlite; 1000 1'. produces. 7

upon adequately. "i'ast cooling, the desired. hardened structure; and reheating to and holding at 1175 1''. results in spheroidisation, which occurs rapidly, as compared to other methods,without harm to the propertiesnormally desired or a spheroldized structure.

The necessary determination or the Asi temperature oi the steel may-be eilected, with suflicient accuracy to carry out the present invention, by austenitizing the steel under question, quenching it violently to render it martensiflc. whereby it has a highly stressed. metastable structure, and then reheating the steelto various temperatures, in the vicinity wheretheAei temperature is anticipated, and quenching untilthe ilrst appearance of untempered msrtensite in a background of martensitetempered by reheating.

The temperature where untempered msrtensite is iirst discernible may be. taken as the Aei temperature oi the steel,

. I claim: I Heating 8. A. nssoosteel to within the range of from 1210' to 1250' 1". and holding it within this range for from two to four hours. cooling at arate atleastasi'astasrfillperhourtoatleast 1050' l". but not so low as to produce martensite.

and reheating the steel to within the range oi from 1150 F. to 1-180 F. and holding it within thisrsnge for from four tosix hours to ,spheroide ize it substantially completely. I r

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